Rhinarium

Rhinarium is the hairless skin area that surrounds the nostrils in many mammals. This surface of the skin is moist. The rhinarium is part of the olfactory system and is therefore associated with the sense of smell. It is thought to be sensitive to pheromones. There is a groove down the middle and it is referred to as a philtrum. Animals with rhinarium are said to have a more acute sense of smell. Nevertheless, rhinarium serves other purposes in certain animals. For instance, in walrus, the rhinarium is covered with bristles that serve as protection especially when the walrus forages for shellfish. The rhinarium is also found to detect wind direction. It enables animals to detect smell with the direction where it came from.1

Having rhinarium is one of the distinctive features that characterize strepsirrhines. Strepsirrhines belong to the suborder Strepsirrhini of the order Primates. The other suborder is Haplorrhini (haplorrhines). The streptorrhines have a rhinarium and are therefore referred to as wet-nosed primates in contrast to the haplorrhines that lack rhinarium (thus, are called dry-nosed primates).